diff --git a/src/google/adk/agents/live_request_queue.py b/src/google/adk/agents/live_request_queue.py
index 9b698c81d6..95ded79bd8 100644
--- a/src/google/adk/agents/live_request_queue.py
+++ b/src/google/adk/agents/live_request_queue.py
@@ -70,6 +70,8 @@ def send_content(self, content: types.Content):
     self._queue.put_nowait(LiveRequest(content=content))
 
   def send_realtime(self, blob: types.Blob):
+    if not blob.mime_type:
+      blob.mime_type = "audio/pcm;rate=16000"
     self._queue.put_nowait(LiveRequest(blob=blob))
 
   def send_activity_start(self):
diff --git a/tests/unittests/agents/test_live_request_queue_issue5584.py b/tests/unittests/agents/test_live_request_queue_issue5584.py
new file mode 100644
index 0000000000..927f0875eb
--- /dev/null
+++ b/tests/unittests/agents/test_live_request_queue_issue5584.py
@@ -0,0 +1,52 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import asyncio
+import unittest
+from unittest.mock import MagicMock
+
+from google.adk.agents.live_request_queue import LiveRequest
+from google.adk.agents.live_request_queue import LiveRequestQueue
+from google.genai import types
+
+
+class TestLiveRequestQueueIssue5584(unittest.IsolatedAsyncioTestCase):
+
+  async def test_send_realtime_default_mime_type(self):
+    queue = LiveRequestQueue()
+    test_data = b"test_audio_data"
+    blob = types.Blob(data=test_data)
+
+    queue.send_realtime(blob)
+    retrieved_request = await queue.get()
+
+    self.assertIsNotNone(retrieved_request.blob)
+    self.assertEqual(retrieved_request.blob.data, test_data)
+    self.assertEqual(retrieved_request.blob.mime_type, "audio/pcm;rate=16000")
+
+  async def test_send_realtime_explicit_mime_type(self):
+    queue = LiveRequestQueue()
+    test_data = b"test_audio_data_opus"
+    explicit_mime_type = "audio/opus"
+    blob = types.Blob(data=test_data, mime_type=explicit_mime_type)
+
+    queue.send_realtime(blob)
+    retrieved_request = await queue.get()
+
+    self.assertIsNotNone(retrieved_request.blob)
+    self.assertEqual(retrieved_request.blob.data, test_data)
+    self.assertEqual(retrieved_request.blob.mime_type, explicit_mime_type)
+
+if __name__ == '__main__':
+  unittest.main()
diff --git a/tests/unittests/agents/test_live_request_queue_mime_type.py b/tests/unittests/agents/test_live_request_queue_mime_type.py
new file mode 100644
index 0000000000..13df856b1c
--- /dev/null
+++ b/tests/unittests/agents/test_live_request_queue_mime_type.py
@@ -0,0 +1,79 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+import asyncio
+from unittest.mock import MagicMock, patch
+
+from google.adk.agents.live_request_queue import LiveRequestQueue, LiveRequest
+from google.genai import types
+
+
+class TestLiveRequestQueueMimeType(unittest.IsolatedAsyncioTestCase):
+
+    def setUp(self):
+        self.live_request_queue = LiveRequestQueue()
+
+    async def test_send_realtime_default_mime_type(self):
+        """
+        Tests that send_realtime sets the default MIME type for audio blobs
+        when no mime_type is explicitly provided.
+        """
+        audio_data = b"some_audio_data"
+        blob = types.Blob(data=audio_data, mime_type=None)
+
+        self.live_request_queue.send_realtime(blob)
+
+        # Retrieve the request from the queue
+        request = await self.live_request_queue.get()
+
+        # Assert that mime_type was set to the default
+        self.assertEqual(request.blob.mime_type, "audio/pcm;rate=16000")
+        self.assertEqual(request.blob.data, audio_data)
+
+    async def test_send_realtime_preserves_explicit_mime_type(self):
+        """
+        Tests that send_realtime preserves an explicitly provided MIME type
+        for audio blobs.
+        """
+        audio_data = b"some_other_audio_data"
+        explicit_mime_type = "audio/opus"
+        blob = types.Blob(data=audio_data, mime_type=explicit_mime_type)
+
+        self.live_request_queue.send_realtime(blob)
+
+        # Retrieve the request from the queue
+        request = await self.live_request_queue.get()
+
+        # Assert that the explicit mime_type was preserved
+        self.assertEqual(request.blob.mime_type, explicit_mime_type)
+        self.assertEqual(request.blob.data, audio_data)
+
+    # Removed test_send_realtime_non_blob_data as send_realtime expects types.Blob
+
+    async def test_send_realtime_blob_with_non_none_mime_type(self):
+        """
+        Tests that send_realtime does not alter mime_type if it's already set to non-None.
+        """
+        audio_data = b"more_audio_data"
+        existing_mime_type = "audio/wav"
+        blob = types.Blob(data=audio_data, mime_type=existing_mime_type)
+
+        self.live_request_queue.send_realtime(blob)
+
+        # Retrieve the request from the queue
+        request = await self.live_request_queue.get()
+
+        self.assertEqual(request.blob.mime_type, existing_mime_type)
+        self.assertEqual(request.blob.data, audio_data)